1. Field of the Invention
The present invention relates to an optical pickup device, and more particularly to an optical pickup device compatible with a multilayer recording medium having a plurality of recording layers for recording information by multi-photon absorption in a laminated direction.
2. Description of the Related Art
In recent years, as the capacity of a recording medium is increased, there has been developed an optical recording medium having a plurality of recording layers in a laminated direction. For instance, the optical recording medium may have an arrangement that the plurality of recording layers and one servo layer are laminated. In this recording medium, a flat recording layer without a guide track is formed, and a servo layer having a guide track is formed on the recording layer. In this arrangement, in performing a recording/reproducing operation, a focusing servo signal and a tracking servo signal are generated based on the guide track formed in the servo layer. Controlling the position of a beam spot on the recording layer based on the servo signals allows the beam spot to scan the recording layer along an intended scanning trajectory.
In an optical pickup device compatible with the recording medium, it is necessary to provide an arrangement for individually and respectively setting servo laser light and recording/reproducing laser light to a servo layer and a recording layer. In this arrangement, since the recording/reproducing laser light is pulled onto the recording layer based on a relation with the servo layer, and subjected to servo control, it is preferable to drive a recording/reproducing objective lens and a servo objective lens with a predetermined cooperative relation to each other, rather than simply driving the objective lenses independently of each other, to cause the recording/reproducing laser light to easily follow a scanning trajectory on a targeted recording layer.
In the case where a plurality of sets of layers each constituted of one servo layer and a plurality of recording layers are arranged in a laminated direction, control may be performed in such a manner that, after servo laser light is pulled onto a targeted recording layer and a servo layer constituting a set of layers with the targeted recording layer, recording/reproducing laser light is pulled onto the targeted recording layer. In this arrangement, by causing the focus position of recording/reproducing laser light to follow the focus position of servo laser light in pulling the servo laser light onto the servo layer, the focus position of recording/reproducing laser light can be set close to the servo layer. This makes it easy to pull the recording/reproducing laser light onto the targeted recording layer, after the servo laser light is pulled onto the servo layer.